Water-based paint composition

ABSTRACT

A water-based paint composition comprising (A) from 10-90% by weight, based on total weight of resin solids of a water-dispersible acrylic graft copolymer having an acid value of 10-30 mg and a hydroxyl value of 50-150, wherein the polymer is obtained by graft polymerization of an acrylic copolymer of an acid value of 35-120 mg KOH/g and a hydroxyl value 50-150 mg KOH/g, and an acrylic copolymer of acid value ≦15 and a hydroxyl value of 50-150, and (B) from 10-90% by weight, based on total weight of resin solids of internally non-crosslinked acrylic fine particles having an acid value 15-200 and a hydroxyl value of 15-200 made by emulsion polymerizing α,β-ethylenically unsaturated monomers.

The present invention relates to a water-based paint composition whichcontains a water-dispersible acrylic graft copolymer and internallynon-crosslinked acrylic fine particles, and especially to a water-basedpaint composition suited to metallic paint for automobiles.

As the problem of pollution of the global environment has deepened inrecent years, international regulations regarding the discharge oforganic solvents have become more and more stringent. Against thisbackground water-based paint using water as a medium has stepped intothe spotlight. In this context, the development of water-based metallicundercoats for industrial painting and especially automobile paintinghas been regarded as advantageous, not only because it has the effect ofdecreasing the use of organic solvents but also from the point of viewof finished appearance and cost-performance, and to date variouswater-based undercoats have been developed.

When one looks at the history of the art of making water-basedundercoats, the trend has been to adopt water-dispersible resins as baseresins. This is because water-based paints in the form of an aqueousdispersion have the advantage of giving the water-based undercoat therheological properties it requires.

Water-based paints in the form of aqueous dispersions are characterizedin that the basic resin is present in the water as particles. These canbe classified broadly into direct emulsions or indirect emulsionsaccording to the method for preparing the basic emulsion. In the directemulsion method particles are formed directly in water by emulsionpolymerization or suspension polymerization; in the indirect emulsionmethod the base resin is first prepared in a solvent phase and thentransferred to an aqueous phase.

Of these the direct emulsion method is very much more efficacious ineliminating solvents from water-based paint since no organic solvent isneeded at the preparation stage, and the preparation of the base resinis also easy. However, because of the limitations imposed by preparingthe base resin in water, it has the problems that the suitability of thestarting materials employed for polymerization has a considerableeffect, and scope for resin design is narrowed.

On the other hand, with the indirect emulsion method there is a largedegree of freedom as to the starting materials which can be employed andwide scope for resin design, but on the other hand there are problems inthat it is difficult to remove the organic solvent employed whenpreparing the base resin, and this hinders the production of low-solventwater-based undercoats.

In this connection, water-based paints using polymer fine particlesobtained by emulsion polymerization are recorded in EP00387 A1 andEP0401565 A1.

However, although such water-based paints do not give rise to paintingfaults such as sagging or bittiness, etc., since the particles conferpseudoplastic or thixotropic properties, there is the problem that theviscosity of the paint is prone to rise after application to the objectto be painted and rheological properties become inadequate, andconsequently smoothness is inferior. They also have the problem thatdispersibility of pigments is inferior and it is difficult to obtainpaint films with an outstanding gloss. Moreover, because the emulsifieris present in the aqueous dispersion after obtaining the resin byemulsion polymerization, inferior water-resistance is a problem.

In Japanese Examined Patent HS-30867 a water-based paint composition isrecorded which contains water-insoluble vinyl resin fine particles ofmean particle size 0.3-6 μm obtained by polymerizing at least one typeof water-soluble resin selected from polyester resins, alkyd resins,vinyl resins, vinyl-modified polyester resins and vinyl-modified alkydresins, with a polymerizable unsaturated monomer in water by two-stageemulsion polymerization in the presence of a seeded emulsion.

However, this water-based paint composition has the problem that becauseit is formed by dispersing a water-insoluble resin storage stability isinferior because it is prone to flocculate.

The purpose of the present invention is to offer a water-based paintcomposition which combines the features both of aqueous dispersion typewater-based paints obtained by direct emulsification and of aqueousdispersion type water-based paints obtained by indirect emulsification:namely, enabling broad scope for design of the base resin andlow-solvent use, not producing blistering, sagging or bittiness, etc.,offering outstanding ease of application and storage stability, and alsoenabling formation of paint films with outstanding water-resistance,durability and smoothness.

A 2nd purpose of the present invention is to offer a water-based paintcomposition suitable as a metallic paint, which confers pseudoplasticand thixotropic properties even when a large quantity of pigment isdispersed therein, does not produce blistering, sagging or bittiness,etc., offers outstanding ease of application, and also enables theformation of paint films with outstanding water-resistance, durabilityand smoothness, and has outstanding storage stability.

The present invention is the following water-based paint compositions.

(1) A water-based paint composition characterized in that it contains

a water-dispersable acrylic graft copolymer (A) which is a graftcopolymer of an acrylic copolymer (a1) which is a copolymer ofα,β-ethylenic unsaturated monomers including an α,β-ethylenicunsaturated carboxylic acid and has an acid value of 35-120 mg KOH/g anda hydroxyl value of 50-150 mg KOH/g, and an acrylic copolymer (a2) whichis a copolymer of α,β-ethylenic unsaturated monomers and has an acidvalue of ≦15 mg KOH/g and a hydroxyl value of 50-150 mg KOH/g, graftedvia chemical bonds, which has an acid value of 10-30 mg KOH/g and ahydroxyl value of 50-150 mg KOH/g, and

internally non-crosslinked acrylic fine particles (B) which are of acopolymer made by emulsion polymerization of α,β-ethylenic unsaturatedmonomers (b1) and have an acid value of 15-200 mg KOH/g and a hydroxylvalue of 15-200 mg KOH/g,

with the proportions within the total resin solids in the water-basedpaint composition which each accounts for being 10-90 wt % for thewater-dispersible acrylic graft copolymer (A), and 10-90 wt % for theinternally non-crosslinked acrylic fine particles (B).

(2) A water-based paint composition recorded in (1) above, characterizedin that it contains an amino resin (C) of a number-average molecularweight of ≦1000, accounting for a proportion of 10-40 wt % of the totalresin solids in the water-based paint composition.

(3) A water-based paint composition recorded in (1) or (2) above,characterized in that it contains an organic thickener swelled byalkalis (D) at 0.1-5 wt % of the total resin solids in the water-basedpaint composition.

(4) A water-based paint composition recorded in any of (1)-(3) above,characterized in that the glass transition temperature of the acryliccopolymer (a1) is -20 to +50° C. and its number average molecular weightis 4500-9000, the glass transition temperature of the water-dispersibleacrylic graft copolymer (A) is -20 to +50° C. and its number averagemolecular weight is 10,000 to 100,000, and that the mean particle sizeof the internally non-crosslinked acrylic fine particles (B) in anaqueous medium is 20-150 nm.

In the present invention the expressions "(meth)acrylic acid" and"(meth)acrylate" indicate "acrylic acid and/or methacrylic acid" and"acrylate and/or methacrylate".

The acrylic graft copolymer (A) used in the present invention is a graftcopolymer in which the main chain is a hydrophilic acrylic copolymer(a1), which is hydrated and becomes a stabilizing layer when dispersedin an aqueous medium, and a hydrophobic acrylic acid copolymer (a2),which becomes a dispersion layer on dispersion, is grafted to this asside chains via chemical bonds.

The acid value of this acrylic graft copolymer (A) is 10-30 mg KOH/g,and preferably 15-30 mg KOH/g, and its hydroxyl value is 50-150 mgKOH/g, and preferably 50-120 mg KOH/g. It is also desirable that theglass transition temperature is -20 to +50° C., and preferably -10 to+30° C., and that the number average molecular weight is 10,000-100,000,and preferably 10,000-50,000.

The acrylic copolymer (a1) which constitutes the main chain of theacrylic graft copolymer (A) is a copolymer of α,β-ethylenic unsaturatedmonomers including an α,β-ethylenic unsaturated carboxylic acid, and hasan acid value of 35-120 mg KOH/g, and preferably 60-110 mg KOH/g, and ahydroxyl value of 50-150 mg KOH/g, and preferably 60-150 mg KOH/g. It isalso desirable that the acrylic copolymer (a1) has a glass transitiontemperature of -20 to +50° C., and preferably -20 to +30° C., and anumber average molecular weight of 4500-9000, and preferably 4800-7000.

The acrylic copolymer (a2) which constitutes the side chains of theacrylic graft copolymer (A) is also a copolymer of α,β-ethylenicunsaturated monomers, and has an acid value of ≦15 mg KOH/g, andpreferably ≦10 mg KOH/g, and a hydroxyl value of 50-150 mg KOH/g, andpreferably 50-120 mg KOH/g.

The acrylic graft copolymer (A) employed in the present invention has astructure in which an acrylic copolymer (a1) and an acrylic copolymer(a2) as described above are graft copolymerized via chemical bonds suchas ester linkages, ether linkages or urethane linkages, etc.

The acrylic graft copolymer (A) employed in the present invention isemployed as the base resin which becomes the film-forming constituent;any polymer which has the aforementioned constitution and propertyvalues can be employed, with no specific restriction as to the methodfor making it. For example, an acrylic graft copolymer (A-1) in which anacrylic copolymer (a2-1) from a monomer combination (mm-1) including anα,β-unsaturated monomer containing a glycidyl group (m-3) and anα,β-unsaturated monomer containing a hydroxyl group (m-4) is graftpolymerized to an acrylic copolymer (a1-1) from an α,β-ethylenicunsaturated monomer containing a hydroxyl group (m-1) and anα,β-ethylenic unsaturated monomer containing a carboxyl group (m-2), oran acrylic graft copolymer (A-2) in which an acrylic copolymer (a2-2)from a monomer combination (mm-2) including copolymerizable unsaturatedmonomers (m-6) is graft polymerized to an acrylic copolymer (a1-2)containing unsaturated bonds, obtained by reacting the acrylic copolymer(a1-1) above with an α,β-ethylenic unsaturated monomer (m-5) containinga functional group which can react with carboxyl groups and/or hydroxylgroups, can be employed as the acrylic graft copolymer (A).

Water-dispersible acrylic graft copolymers (A-1) which can be employedas a preferred Component (A) will first be explained. In acrylic graftcopolymers of (A-1), an α,β-ethylenic unsaturated monomer (m-1)containing a hydroxyl group and an α,β-ethylenic unsaturated monomer(m-2) containing a carboxyl group are essential components of thehydrophilic acrylic copolymer (a1) which becomes the stabilizing layer;and the acrylic graft copolymer (a1-1) can be made from theseα,β-ethylenic unsaturated monomers and any other optionally usedcopolymerizable unsaturated monomer(s) (m-7) by a known solutionpolymerization method in the presence of a suitable polymerizationinitiator.

Examples of α,β-ethylenic unsaturated monomers (m-1) containing ahydroxyl group include hydroxyalkyl esters of (meth)acrylic acid, suchas 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate and3-hydroxypropyl (meth)acrylate, etc., polyether polyols such aspolyethylene glycol and polypropylene glycol, etc., monoethers ofα,β-unsaturated monomers containing a hydroxyl group such as2-hydroxyethyl (meth)acrylate, etc., and lactone-modified α,β-ethylenicunsaturated monomers such as addition compounds of hydroxyalkyl estersof (meth)acrylic acid with 1-10 mols of a lactone such as ε-caprolactoneor γ-caprolactone, etc. These can be employed singly or in combinationsof 2 or more.

Examples of α,β-ethylenic unsaturated monomers (m-2) containing acarboxyl group include acrylic acid, methacrylic acid, crotonic acid,itaconic acid and maleic acid, etc. These can be employed singly or incombinations of 2 or more.

Other optionally used copolymerizable unsaturated monomers (m-7)include: esters, for example C₁₋₁₈ alkyl esters of (meth)acrylic acid,such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl(meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, hexyl(meth)acrylate, octyl (meth)acrylate and lauryl (meth)acrylate, etc.;alkoxyalkyl esters of (meth)acrylic acid, such as methoxybutyl acrylate,methoxyethyl (meth)acrylate and ethoxybutyl (meth)acrylate, etc.; amidesof acrylic acid and methacrylic acid; (meth)acrylic acid amides such asN-methylol(meth)acrylamide and N-isobutoxymethylol(meth)acrylamide,etc.; and aromatic vinyl compounds such as styrene, α-methylstyrene andvinyltoluene, etc.

The acrylic copolymers (a1-1) can be obtained by solution polymerizationaccording to an ordinary method using these monomers, in the presence ofa known polymerization initiator, such as azobisisobutyronitrile,benzoyl peroxide, t-butyl peroxybenzoate, t-butyl peroxide ort-butylperoxy-2-ethylhexanoate, etc. This reaction is performed suchthat the acrylic copolymer (a1-1) produced has an acid value of 35-120mg KOH/g, and preferably 50-110 mg KOH/g and a hydroxyl value of 50-150mg KOH/g, and preferably 60-150 mg KOH/g. It is also desirable that thereaction is performed to give a glass transition temperature of -20 to+50° C., and preferably -20 to +30° C., and a number average molecularweight of 4500-9000, and preferably 4800-7000. As the reaction medium,toluene, methyl isopropyl ketone, ethylene glycol monoethyl ether,ethylene glycol monobutyl ether, propylene glycol monopropyl ether orpropylene glycol monoethyl ether, etc., or a mixture of these, etc., canbe employed.

When the acid value of the acrylic copolymer (a1-1) is less than 35 mgKOH/g its action as a stabilizing layer is inadequate and the resultingacrylic graft copolymers (A-1) become prone to flocculate in an aqueousmedium so that storage stability is inferior; and when it exceeds 120 mgKOH/g it becomes too hydrophilic and paint films formed from water-basedpaint compositions prepared from the resulting acrylic graft copolymers(A-1) are inferior in water-resistance.

When the hydroxyl value of the acrylic copolymer (a1-1) is less than 50mg KOH/g there are insufficient points for crosslinking between theresulting acrylic graft copolymers (A-1) and the amino resin (C) used asa curing agent, and consequently paint films obtained are inferior inresistance to chemicals; and when it exceeds 150 mg KOH/g the resultingacrylic graft copolymers (A-1) become excessively hydrophilic, and paintfilms formed from water-based paint compositions containing them areinferior in water-resistance.

Similarly, when the glass transition temperature of the acryliccopolymer (a1-1) is less than -20° C. the resulting acrylic graftcopolymers (A-1) are prone to conglutinate in aqueous media, so that thestorage stability of aqueous dispersions is inferior; and when the glasstransition temperature exceeds +50° C. the resulting acrylic graftcopolymers (A-1) have a high softening point, and the smoothness ofpaint films from water-based paint compositions prepared from these isinferior.

When the number average molecular weight of the acrylic copolymer (a1-1)is less than 4500 it cannot form an adequate stabilizing layer and thestorage stability of aqueous dispersions of resulting acrylic graftcopolymers (A-1) is inferior; and when it exceeds 9000 aqueousdispersions of the resulting graft copolymers (A-1) become highlyviscous, the proportion of painted solids of water-based paintcompositions prepared from these is lowered and they are inferior asregards sagging.

The acrylic graft copolymer (A-1) is obtained by reacting a monomercombination (mm-1) with the acrylic copolymer (a1-1) above. As themonomer combination (mm-1) a monomer combination is employed in whichthe essential components are an α,β-ethylenic unsaturated monomer (m-3)containing a glycidyl group and an α,β-ethylenic unsaturated monomer(m-4) containing a hydroxyl group, combined if necessary with (an)othercopolymerizable unsaturated monomer(s) (m-7), to give an acid value of≦15 mg KOH/g, and preferably ≦10 mg KOH/g, and a hydroxyl value of50-150 mg KOH/g and preferably 50-120 mg KOH/g.

Examples of α,β-ethylenic unsaturated monomers (m-3) containing aglycidyl group include glycidyl (meth)acrylate and allyl glycidyl ether,etc. Examples of α,β-ethylenic unsaturated monomers containing ahydroxyl group (m-4) and of other copolymerizable unsaturated monomers(m-7) have been cited in connection with the aforementioned acryliccopolymer (a1-1).

When the acid value of the monomer combination (mm-1) above exceeds 15mg KOH/g the resulting acrylic graft copolymers (A-1) become highlyviscous, the proportion of painted solids of water-based paintcompositions prepared from these is lowered and they are inferior asregards sagging.

When the hydroxyl value of the monomer combination (mm-1) is less than50 mg KOH/g there are insufficient points for crosslinking between theresulting acrylic graft copolymers (A-1) and the amino resin (C) used asa curing agent, and consequently paint films obtained are inferior inresistance to chemicals; and when it exceeds 150 mg KOH/g the resultingacrylic graft copolymers (A-1) become excessively hydrophilic, and theresulting paint films are inferior in water-resistance.

The reaction between the aforementioned acrylic copolymer (a1-1) andmonomer combination (mm-1) is performed with a ratio of acryliccopolymer (a1-1) and monomer combination (mm-1), (a1-1)/(mm-1) (w/w) of10/90 to 60/40, and preferably 20/80 to 40/60, and (m-3)/(a1-1)(mol/mol) 0.4-1.5, and preferably 0.8-1.2.

The number of mols of acrylic copolymer (a1-1) can be decided bycalculation from the number average molecular weight (polystyrene basis)determined in the ordinary way by gel permeation chromatography.

When (a1-1)/(mm-1) (w/w) is less than 10/90 an adequate stabilizinglayer is not formed, and aqueous dispersions of the resulting acrylicgraft copolymers (A-1) have inferior storage stability; and when itexceeds 60/40 aqueous dispersions of the resulting acrylic graftcopolymers (A-1) become very highly viscous, the proportion of paintedsolids of water-based paint compositions prepared from these acrylicgraft copolymers (A-1) is lowered and they are inferior as regardssagging.

Similarly, when the molar ratio of the quantity of α,β-ethylenicunsaturated monomer (m-3) containing a glycidyl group in the combinationrelative to the acrylic copolymer (a1-1) is less than 0.4, the graftingreaction with the monomer combination (mm-1) becomes inadequate, andeither dispersion of the resulting acrylic graft copolymer (A-1) in anaqueous medium becomes difficult, or the storage stability of theresulting water-based paint composition is inferior; and when it exceeds1.5 gelling occurs and it is impossible to make an acrylic graftcopolymer (A-1).

The reaction between the acrylic copolymer (a1-1) and the monomercombination (mm-1) can be performed by graft copolymerizing! the acrylicgraft copolymer (a1-1) and the monomer combination (mm-1) by a knownsolution polymerization method in an organic solvent. Thus, it can beperformed by a known solution polymerization method in an organicsolvent as a continuation of the preparation of the acrylic copolymer(a1-1) by adding the monomer combination to the reaction liquor aftermaking the acrylic copolymer (a1-1).

As the organic solvent, toluene, methyl isopropyl ketone, ethyleneglycol monoethyl ether, ethylene glycol monobutyl ether, propyleneglycol monopropyl ether or propylene glycol monoethyl ether, etc., or amixture of these, etc., can be employed.

As the polymerization initiator for copolymerizing the monomercombination (mm-1) the same polymerization initiators given as examplesin the making of the acrylic copolymer (a1-1) can be employed.

It is desirable that the combined concentration of acrylic copolymer(a1-1) and monomer combination (mm-1) in the reaction solution is 30-90wt %, and preferably 50-80 wt %, and that the concentration of thepolymerization initiator is 0.1-10 wt %, and preferably 0.5-5 wt %. Itis also desirable that the reaction temperature is 20-180° C., andpreferably 40-160° C., and that the reaction time is 1-10 hours.

The acid value, hydroxyl value, glass transition temperature and numberaverage molecular weight of the resulting acrylic graft copolymer (A-1)can be adjusted by selecting the reaction conditions such as the typesof acrylic copolymer (a1-1) and monomer combination (mm-1) employed andthe quantities employed, the reaction temperature, the reaction time andthe type and quantity of polymerization initiator employed.

In the reaction above graft polymerization is performed by ring openingaddition which proceeds between the carboxyl groups of the acryliccopolymer (a1-1) and the glycidyl groups of the component (m-3) whichcontains a glycidyl group, and accompanying free radical polymerizationof the different monomers (m-3), (m-4) and (m-7), to make an acrylicgraft copolymer (A-1) in a single-stage reaction.

The acrylic graft copolymer (A-1) is a graft copolymer which can be madeas described above, and is a water-dispersible acrylic graft copolymerwhich has an acid value of 10-30 mg KOH/g, and preferably 15-30 mgKOH/g, and a hydroxyl value of 50-150 mg KOH/g, and preferably 50-120 mgKOH/g. It is also desirable that this acrylic graft copolymer (A-1) hasa glass transition temperature of -20 to +50° C., and preferably -10 to+30° C., and a number average molecular weight of 10,000-100,000 andpreferably 10,000-50,000.

When the acid value of the acrylic graft copolymer (A-1) is less than 10mg KOH/g it becomes difficult to disperse in an aqueous medium, orstorage stability is inferior; and when it exceeds 30 mg KOH/g theresulting aqueous dispersions become very highly viscous, the proportionof painted solids of water-based paint compositions prepared from theseis lowered and they are inferior as regards sagging.

When the hydroxyl value of the acrylic graft copolymer (A-1) is lessthan 50 mg KOH/g there are insufficient points for crosslinking betweenthe resulting acrylic graft copolymers (A-1) and the amino resin (C)used as a curing agent, and consequently paint films obtained areinferior in resistance to chemicals; and when it exceeds 150 mg KOH/g itbecomes excessively hydrophilic and the paint films obtained areinferior in water-resistance.

Similarly, when the glass transition temperature of the acrylic graftcopolymer (A-1) is less than -20° C. the graft copolymer (A-1) is proneto conglutinate in aqueous media, so that the storage stability ofaqueous dispersions is inferior; and when the glass transitiontemperature exceeds +50° C. the smoothness of paint films fromwater-based paint compositions containing this acrylic graft copolymer(A-1) is inferior.

When the number average molecular weight of the acrylic graft copolymer(A-1) is less than 10,000 paint films formed from water-based paintcompositions prepared from this acrylic graft copolymer (A-1) areinferior in resistance to chemicals; and when it exceeds 100,000 thereis a risk that gelling will occur when making the acrylic graftcopolymer.

Aforementioned acrylic graft copolymers (A-2) which can be employed aspreferred components (A) will next be explained. Acrylic graftcopolymers (A-2) are graft copolymers in which an acrylic copolymer(a1-2) containing unsaturated bonds, obtained by reacting anaforementioned acrylic copolymer (a1-1) with an α,β-ethylenicunsaturated monomer (m-5) having a functional group which can react withcarboxyl groups and/or hydroxyl groups, and a monomer combination (mm-2)comprising copolymerizable unsaturated monomers (m-6), are graftpolymerized.

As regards the α,β-ethylenic unsaturated monomers (m-5) above, concreteexamples of α,β-ethylenic unsaturated monomers (m-5-1) which have afunctional group which can react with hydroxyl groups includeα,α-dimethylisopropenylbenzyl isocyanate and methacryloyl isocyanate,etc. Concrete examples of α,β-ethylenic unsaturated monomers (m-5-2)which have a functional group which can react with carboxyl groupsinclude glycidyl (meth)acrylate and allyl glycidyl ether, etc.

The reaction between the acrylic copolymer (a1-1) and a monomer (m-5)above is performed with a molar ratio (m-5)/(a1-1) of 0.4-1.5, andpreferably 0.8-1.2, such that the acrylic copolymer (a1-2) containingunsaturated bonds that is obtained has an acid value of 35-120 mg KOH/g,and preferably 50-150 mg KOH/g sic!, and a hydroxyl value of 50-150 mgKOH/g, and preferably 60-150 mg KOH/g. It is also desirable that thereaction is performed to give a glass transition temperature of -20 to+50° C., and preferably -20 to +30° C., and a number average molecularweight of 4500-9000, and preferably 4800-7000. The number of mols ofacrylic copolymer (a1-1) can be decided by calculation from the numberaverage molecular weight (polystyrene basis) determined in the ordinaryway by gel permeation chromatography.

When the mol ratio above is less than 0.4 the grafting reaction with themonomer combination (mm-2) becomes inadequate, and either dispersion ofthe resulting acrylic graft copolymer (A-2) in an aqueous medium becomesdifficult, or the storage stability of the resulting water-based paintcomposition is inferior; and when it exceeds 1.5 gelling occurs and itis impossible to make an acrylic graft copolymer (A-2).

When the acid value of the acrylic copolymer (a1-2) is less than 35 mgKOH/g its action as a stabilizing layer is inadequate and the resultingacrylic graft copolymers (A-2) become prone to flocculate in an aqueousmedium so that storage stability is inferior; and when it exceeds 120 mgKOH/g it becomes too hydrophilic and paint films formed from water-basedpaint compositions prepared from the resulting acrylic graft copolymers(A-2) are inferior in water-resistance.

When the hydroxyl value of the acrylic copolymer (a1-2) is less than 50mg KOH/g there are insufficient points for crosslinking between theresulting acrylic graft copolymers (A-2) and the amino resin (C) used asa curing agent, and consequently paint films obtained are inferior inresistance to chemicals; and when it exceeds 150 mg KOH/g the resultingacrylic graft copolymers (A-2) become excessively hydrophilic and paintfilms formed from water-based paint compositions containing them areinferior in water-resistance.

Similarly, when the glass transition temperature of the acryliccopolymer (a1-2) is less than -20° C. the acrylic graft copolymers (A-2)obtained are prone to conglutinate in aqueous media, so that the storagestability of aqueous dispersions is inferior; and when the glasstransition temperature exceeds +50° C. the resulting acrylic graftcopolymers (A-2) have a high softening point, and the smoothness ofpaint films from water-based paint compositions prepared from these isinferior.

When the number average molecular weight of the acrylic copolymer (a1-2)is less than 4500 it cannot form an adequate stabilizing layer and thestorage stability of aqueous dispersions of resulting acrylic graftcopolymers (A-2) is inferior; and when it exceeds 9000 aqueousdispersions of the resulting graft copolymers (A-2) become highlyviscous, the proportion of painted solids of water-based paintcompositions prepared from these is lowered and they are inferior asregards sagging.

The reaction of the acrylic copolymer (a1-1) and the monomer (m-5) ispreferably performed in the presence of a catalyst such as dibutyltindiacetate, dibutyltin dilaurate or dibutyltin diacetonate, etc.

It is desirable that the combined concentration of component (a1-1) andcomponent (m-5) in the reaction solution is 30-90 wt %, and preferably50-80 wt %, and that the concentration of catalyst in the reactionliquid is 0.1-5 wt %, and preferably 0.1-2 wt %. It is also desirablethat the reaction temperature is 20-120° C., and preferably 40-140° C.,and the reaction time is 0.5-5 hours.

In the reaction above an acrylic copolymer (a1-2) containing unsaturatedbonds is made by reaction between the hydroxyl groups of the acryliccopolymer (a1-1) and the functional group of component (m-5) whichreacts with carboxyl groups or hydroxyl groups, for example anisocyanate group or a glycidyl group, to form chemical bonds by whichcomponent (m-5) is added to the acrylic copolymer (a1-1).

The acrylic graft copolymer (A-2) is obtained by graft copolymerizing toan acrylic copolymer (a1-2) containing unsaturated bonds above a monomercombination (mm-2) combining copolymerizable unsaturated monomers (m-6)to give an acid value of ≦15 mg KOH/g, and preferably ≦10 mg KOH/g, anda hydroxyl value of 50-150 mg KOH/g, and preferably 60-120 mg KOH/g.

The copolymerizable unsaturated monomers (m-6) can be selected from theα,β-ethylenic unsaturated monomers (m-1) containing a hydroxyl group,α,β-ethylenic monomers (m-2) containing a carboxyl group and othercopolymerizable unsaturated monomers (m-7) given as examples inconnection with the aforementioned acrylic copolymer (a1-1).

When the acid value of the monomer combination (mm-2) above exceeds 15mg KOH/g the resulting acrylic graft copolymers (A-2) become highlyviscous, the proportion of painted solids of water-based paintcompositions prepared from these is lowered and they are inferior asregards sagging.

When the hydroxyl value of the monomer combination (mm-2) is less than50 mg KOH/g there are insufficient points for crosslinking between theresulting acrylic graft copolymers (A-2) and the amino resin (C) used asa curing agent, and consequently paint films obtained are inferior inresistance to chemicals; and when it exceeds 150 mg KOH/g it becomesexcessively hydrophilic, and the resulting paint films are inferior inwater-resistance.

The reaction between the aforementioned acrylic copolymer (a1-2)containing unsaturated bonds and monomer combination (mm-2) is performedwith a ratio of acrylic copolymer (a1-2) containing unsaturated bondsand monomer combination (mm-2), (a1-2)/(mm-2) (w/w) of 10/90 to 60/40,and preferably 20/80 to 40/60, and (m-3)/(a1-1) (mol/mol) 0.4-2.5, andpreferably 0.8-2.2. When this weight ratio is less than 10/90 anadequate stabilizing layer is not formed, and aqueous dispersions of theresulting acrylic graft copolymers (A-2) have inferior storagestability; and when it exceeds 60/40 aqueous dispersions of theresulting acrylic graft copolymers (A-2) become very highly viscous, theproportion of painted solids of water-based paint compositions preparedfrom these acrylic graft copolymers (A-2) is lowered and they areinferior as regards sagging.

The reaction between the acrylic copolymer (a1-2) and the monomercombination (mm-2) can make component (a1-2) and the monomer combination(mm-2) by a known solution polymerization method in a suitable reactionmedia.

The graft polymerization reaction between component (a1-2) and component(mm-2) can be performed in the presence of a polymerization initiator bya known method. As the polymerization initiator the same polymerizationinitiators given as examples in the making of the acrylic copolymer(a1-1) can be employed.

It is desirable that the combined concentration of acrylic copolymer(a1-2) and monomer combination (mm-2) in the reaction solution is 30-90wt %, and preferably 50-80 wt %, and that the concentration of thepolymerization initiator is 0.1-10 wt %, and preferably 0.5-5 wt %,relative to the total weight. It is also desirable that the reactiontemperature is 20-180° C., and preferably 40-160° C., and that thereaction time is 1-10 hours.

The acid value, hydroxyl value, glass transition temperature and numberaverage molecular weight of the resulting acrylic graft copolymer (A-2)can be adjusted by selecting the reaction conditions such as the typesof component (a1-2) and component (mm-2) employed and the quantitiesemployed, the reaction temperature, the reaction time and the type andquantity of polymerization initiator employed.

In the reaction above graft polymerization is performed bycopolymerization of the monomer combination (mm-2) with the unsaturatedbonds in component (a1-2), to make the acrylic graft copolymer (A-2).

The acrylic graft copolymer (A-2) is a graft copolymer which can be madeas described above, and is a water-dispersible acrylic graft copolymerwhich has an acid value of 10-30 mg KOH/g, and preferably 15-30 mgKOH/g, and a hydroxyl value of 50-150 mg KOH/g, and preferably 60-120 mgKOH/g. It is also desirable that this acrylic graft copolymer (A-2) hasa glass transition temperature of -20 to +50° C., and preferably -10 to+30° C., and a number average molecular weight of 10,000-100,000 andpreferably 10,000-50,000.

When the acid value of the acrylic graft copolymer (A-2) is less than 10mg KOH/g it becomes difficult to disperse in an aqueous medium, orstorage stability is inferior; and when it exceeds 30 mg KOH/g theresulting aqueous dispersions become very highly viscous, the proportionof painted solids of water-based paint compositions prepared from theseis lowered and they are inferior as regards sagging.

When the hydroxyl value of the acrylic graft copolymer (A-2) is lessthan 50 mg KOH/g there are insufficient points for crosslinking betweenthe resulting acrylic graft copolymers (A-2) and the amino resin (C)used as a curing agent, and consequently paint films obtained areinferior in resistance to chemicals; and when it exceeds 150 mg KOH/g itbecomes excessively hydrophilic, and the paint films obtained areinferior in water-resistance.

Similarly, when the glass transition temperature of the acrylic graftcopolymer (A-2) is less than -20° C. the acrylic graft copolymer (A-2)is prone to conglutinate in aqueous media, so that the storage stabilityof aqueous dispersions is inferior; and when the glass transitiontemperature exceeds +50° C. the smoothness of paint films fromwater-based paint compositions containing this acrylic graft copolymer(A-2) is inferior.

When the number average molecular weight of the acrylic graft copolymer(A-2) is less than 10,000 paint films formed from water-based paintcompositions prepared from this acrylic graft copolymer (A-2) areinferior in resistance to chemicals; and when it exceeds 100,000 thereis a risk that gelling will occur when making the acrylic graftcopolymer.

The acrylic graft copolymers (A) such as (A-1) and (A-2) employed in thepresent invention can be made into aqueous dispersions by neutralizingwith a basic substance and dispersion in an aqueous dispersion medium,after removing the solvent employed in making them if necessary.Dispersion in an aqueous dispersion medium can be performed by anordinary method: it can be performed for example by neutralizing atleast 50% of the carboxyl groups present in the acrylic graft copolymer(A) by using monomethylamine, dimethylamine, trimethylamine,diethylenetriamine, diethanolamine, dimethylethanolamine, piperazine,ammonia or sodium hydroxide, etc., for example as a basic substance. Anaqueous dispersion medium in which water accounts for 40-80 wt % ispreferred.

An aqueous dispersion thus obtained can be combined as it stands, orafter concentration or dilution or drying and resuspension, withinternally non-crosslinked acrylic fine particles (B), an amino resin(C) and an alkali-swelling organic extender (D) described below, etc.,to prepare a water-based paint composition.

The internally non-crosslinked fine particles (B) employed in thepresent invention are internally non-crosslinked fine particles made byperforming free radical polymerization of α,β-ethylenic unsaturatedmonomers (b1) by a known emulsion polymerization method in an aqueousmedium in the presence of a surfactant, and besides being employed as abasic resin which becomes the film-forming component of the water-basedpaint composition, are a component which confers pseudoplastic orthixotropic properties on the water-based paint composition.

The copolymerization here can be performed with an α,β-ethylenicunsaturated monomer (b1-1) containing a carboxyl group and anα,β-ethylenic unsaturated monomer (b1-2) containing a hydroxyl group asessential components, and other copolymerizable monomers as required. Asthese monomers the same monomers indicated in connection with theaforementioned acrylic copolymer (a1-1) can be employed.

There is no specific restriction as to the method for emulsionpolymerization, examples of which include seeded polymerization, 2-stageemulsion polymerization, 2-stage polymerization in the presence of aseeded emulsion, and the power feed method, etc.

The surfactant employed for emulsion polymerization is preferably ananionic or non-ionic surfactant. Examples of such surfactants includesodium dodecylbenzenesulfonate, ammonium dodecylbenzenesulfonate,ammonium polyoxyethylene lauryl ether sulfate, sodiumalkylphenylpolyoxyethylene sulfate, ammonium alkylphenylpolyoxyethylenesulfate, polyoxyethylene oleyl ether and polyoxyethylene tridecyl ether,etc. The quantity of surfactant added will differ depending on theemulsifying capacity of the surfactant employed and the particle size ofthe internally non-crosslinked acrylic fine particles (B) to be obtainedas a result, but it is generally in the range 0.05-5 wt %, andpreferably 0.1-4 wt % relative to the water.

There is no specific restriction as to the polymerization initiatoremployed for emulsion polymerization, and organic peroxides, inorganicperoxides, azo type polymerization initiators and redox typepolymerization initiators can be employed: examples include benzoylperoxide, t-butyl peroxybenzoate, t-butyl peroxyoctanoate, ammoniumpersulfate, sodium persulfate, and the ferrous salt of hydrogenperoxide, etc.

The internally non-crosslinked acrylic fine particles employed areparticles (B) having an acid value of 15-200 mg KOH/g, and preferably20-100 mg KOH/g, and a hydroxyl value of 15-200 mg KOH/g, and preferably20-100 mg KOH/g. It is also desirable that particles with a glasstransition temperature a -20 to +50° C., and preferably 0 to +30° C.,and a mean particle size in an aqueous medium of 20-150 nm, andpreferably 50-100 nm, are employed.

When the acid value is less than 15 mg KOH/g there is a proneness toflocculate, so that the storage stability of the water-based paintcomposition is inferior. The benefits in conferring pseudoplastic orthixotropic properties on the water-based paint composition are alsoweakened, aluminum bittiness is prone to be produced and ease ofapplication is inferior. On the other hand, when the acid value exceeds200 mg KOH/g they become excessively hydrophilic and thewater-resistance of the resulting paint films is inferior.

When the hydroxyl value is less than 15 mg KOH/g there are insufficientpoints of crosslinking with the amino resin (C) and the resulting paintfilms are inferior in chemical resistance; and when the hydroxyl valueexceeds 200 mg KOH/g they become excessively hydrophilic andconsequently the water-resistance of the resulting paint films isinferior.

Similarly, when the glass transition temperature is less than -20° C.the acrylic fine particles (B) are prone to conglutinate in aqueousmedia, so that the storage stability of aqueous dispersions is inferior;and when the glass transition temperature exceeds 50° C. the smoothnessof paint films is inferior.

When the particle size of the acrylic fine particles (B) is less than 20nm a large quantity of surfactant is necessary for making them andtherefore the water-resistance of the resulting paint films is inferior.On the other hand, when the particle size exceeds 150 nm the surfacearea effect of the acrylic fine particles (B) is considerably decreased,the benefits in conferring pseudoplastic or thixotropic properties onthe water-based paint compositions are weakened, aluminum bittiness isprone to be produced and ease of application is inferior.

The amino resin (C) employed in the present invention is an amino resinof a number average molecular weight of ≦1000, and preferably 300-800,and is the crosslinking component (curing agent) of the water-basedpaint composition. Examples of such amino resins (C) include thecommercial products Cymel 301, Cymel 303, Cymel 325 and Cymel 327 (tradenames Mitsui Scitec KK), Nikalac MW-30 and Nikalac MX43 (trade namesSanwa Chemical KK) and Yuban 120 (trade name Mitsui Toatsu Chemicals),etc. The number average molecular weight of the amino resin (C) is thenumber average molecular weight based on polystyrene, determined bygel-permeation chromatograph according to the normal method. When thenumber average molecular weight (C) of the amino resin (C) exceeds 1000it is difficult to disperse in aqueous media and the stability of thewater-based paint composition is inferior.

The organic thickener swelled by alkalis (D) employed in the presentinvention is a component which confers further pseudoplastic orthixotropic properties on the water-based paint composition, and it isparticularly efficacious when including a phosphorescent pigment in thewater-based paint composition as in metallic paint compositions.Examples of organic thickeners swelled by alkalis (D) include ASE-60(trade name Rohm and Haas) and Thickensol-150B (trade name KyoeiChemical), etc.

Water-based paint compositions of the present invention comprise aqueousdispersions containing an aforementioned water-dispersible acrylic graftco-polymer (A) and internally non-crosslinked acrylic fine particles (B)as essential components, and optionally also an amino resin (C) and/or athickener swelled by alkalis (D).

When it does not contain component (C) the contents of component (A) andcomponent (D) in the total resin solids of the water-based paintcomposition are 10-90 wt %, and preferably 40-80 wt %, for component (A)and 10-90 wt %, and preferably 20-60 wt % for component (B). When itcontains (C) there is 20-80 wt %, and preferably 30-70 wt %, ofcomponent (A), 20-80 wt %, and preferably 30-70 wt %, of component (B),and 10-40 wt %, and preferably 20-40 wt %, of component (C).

The content of component (D) is 0.1-5 wt %, and preferably 0.5-4 wt %,of the total resin solids in the water-based paint composition.

With less than the lower limit of component (A) the primary resin in thewater-based paint composition is inadequate and the basic performance ofthe resulting paint film is inferior. On the other hand, when it exceedsthe upper limit above the action of component (B) is considerablydamaged and ease of application of the water-based paint composition isinferior.

With less than the lower limit of component (B) the benefits in terms ofconferring pseudoplasticity or thixotropy on the water-based paintcomposition are weakened and ease of application is inferior. On theother hand, when it exceeds the upper limit above, the quantity ofsurfactant included in the water-based paint composition is increasedand the water-resistance of the resulting paint film is inferior.

When component (C) is within the range above, the resulting paint filmshow even better resistance to chemicals and resilience than whencomponent (C) is not included.

Component (D) is efficacious in the preparation of metallic paintcompositions; when the content thereof is less that 0.1 wt % bittinessis produces, and when it exceeds 5 wt % the water-resistance of thepaint film is inferior because of the high acid value of component (D).

Organic solvents can optionally be added to a water-based paintcomposition of the present invention. Examples of such organic solventsinclude ethylene glycol monoethyl ether, ethylene glycol monobutylether, diethylene glycol mo no!butyl ether, ethylene glycol monohexylether, propylene glycol monomethyl ether, propylene glycol monoethylether and propylene glycol monobutyl ether, etc.

Metallic pigments, inorganic pigments and/or organic pigments, etc., canalso optionally be added. There is no specific restriction as to themethod of adding pigments, and this can be performed by a known method.Moreover, other known additives added to water-based paints, such asacid catalysts, surface regulators and/or blistering inhibitors, etc.,can also optionally be included.

Water-based paint compositions of the present invention have extremelyoutstanding storage stability, there are easy to apply because they havepseudoplastic and/or thixotropic properties, and paint films obtainedfrom them have excellent paint film performance traits such aswater-resistance, durability and smoothness, etc.

Water-based paint compositions of the present invention can primarily beemployed as undercoats for automobiles, and in this case they can behandled in the same way as ordinary undercoats, and they canparticularly suitably be employed in prior known 2-coats 1-bake paintingsystems in which the undercoat and the top coat are applied wet-on-wetand then the two are baked at the same time.

The benefits recorded in the present invention can be obtained when thevarious numerical ranges hitherto explained, for example the propertyvalues of the acrylic copolymers and monomer combinations, theproportions in which they are reacted, the property values of theacrylic graft copolymer (A), and the contents of components (A)-(D),etc., are in the ranges recorded; and particularly outstanding benefitscan be obtained when the numerical ranges of the different values arethe ranges defined as the preferred ranges.

By using as the base resin an acrylic graft copolymer (A) in which acomponent of high acid value and a component of low acid value arechemically linked, and further including internally non-crosslinkedacrylic fine particles (B), water-based paint compositions of thepresent invention allow broad scope for base resin design and lowsolvent use, they do not produce blistering, sagging or bittiness, andthey give paint films of outstanding water-resistance, durability andsmoothness etc.

Including an amino resin (C) in a water-based paint composition of thepresent invention further improves the resilience of the paint film andits resistance to chemicals.

Including a thickener swelled by alkalis (D) in a water-basedcomposition of the present invention confers further pseudoplasticityand thixotropy when phosphorescent pigments are included as in ametallic paint composition, and improves ease of application.

The present invention will next be explained in even more detail bymeans of practical embodiments; however, these embodiments do not implyany restrictions as to the scope of the present invention. In theexamples "parts" indicates "parts by weight" except where specificallystated otherwise. The method of application and the methods forevaluating paint film appearance, paint film performance and storagestability are as follows.

The following were used as test sheets to be painted. Thus, sheet steeltreated with zinc phosphate, electrocoated with a cathodic depositionpaint (Aqua No. 4200; trade name Nippon Oil & Fats) to give a dry filmthickness of 20 μm, baked at 175° C. for 20 minutes, air sprayed with amiddle coat paint (Haiepiko No. 100 CP Sealer; trade name Nippon Oil &Fats) to give a dry film thickness of 40 μm and baked at 140° C. for 20minutes was used.

These test sheets were painted with the water-based paint compositionsprepared in the different examples by the known 2-coats 1-bake method.Thus, the water-based paint composition was spray-coated in a paintingenvironment at a temperature of 25° C. and a relative humidity of 75% togive a dry film thickness of approximately 15 μm, followed by drying byheating at a temperature of 80° C. for 10 minutes, cooling to roomtemperature, and then spray coating with a commercial clear top coat(Belcoat No. 6000; trade name Nippon Oil & Fats) to give a dry filmthickness of approximately 40 μm followed, after setting for 10 minutes,by baking at 140° C. for 30 minutes. The object to be painted was heldperpendicular throughout the entire process.

1) 60° Gloss

JIS K5400 (1990) 7.6 mirror-surface gloss.

2) Smoothness

The paint film was observed visually and evaluated using the followingcriteria.

∘: satisfactory

×: inferior

3) Aluminum bittiness

The paint film was observed visually and evaluated using the followingcriteria.

∘: no bittiness

×: bittiness

4) Sagging

A hole 10 mm in diameter was opened in the object to be painted and thelength of sagging under the hole after painting to give a dry filmthickness of 20 μm was assessed according to the following criteria.

∘: less than 2 mm

×: ≧2 mm

1) Water-resistance

The state of the painted surface was observed visually after immersionfor 4 hours in hot water at 90° C., and evaluated according to thefollowing criteria.

∘: no abnormality

×: blistering

2) Resistance to chemicals

The state of the painted surface was observed visually after immersionfor 1 hour in regular petrol at 40° C., and evaluated according to thefollowing criteria.

∘: no abnormality

×: shrinkage

3) Resilience

Evaluated by JIS K5400 (1990) 8.3 Dupont impact resistance, assessedaccording to the following criteria after dropping the weight from aheight of 20 cm.

∘: not able to be cracked or detached

×: cracking or detachment produced

Evaluated by the change (%) in viscosity of the water-based paintcomposition after storage at 40° C. for 20 days compared with initialviscosity (ps/6 rpm (B type viscosimeter)), according to the followingcriteria.

∘: less than ±15%

×: ≧+15%

Preparation Example 1-1

Making an Acrylic Graft Copolymer (A-1)

Methyl isopropyl ketone 56.4 parts was put into a reaction vesselequipped with a stirrer, a temperature regulator, a cooling tube and adropping device, stirred as the temperature was raised, and refluxed. Amixture of 41.8 parts of 2-hydroxyethyl methacrylate, 11.6 parts ofacrylic acid, 93.6 parts of n-butyl acrylate, 33.0 parts of 2-ethylhexylmethacrylate and 3.6 parts of azobisisobutyronitrile was then addeddropwise over 2 hours. Stirring under reflux was continued for a further2 hours to complete the polymerization (this reaction process is termed"Process 1" hereafter).

The resin obtained was an acrylic copolymer having an acid value of 50mg KOH/g, a hydroxyl value of 100 mg KOH/g, a glass transitiontemperature of -20° C. and a number average molecular weight of 5000.

A further 328.6 parts of methyl isobutyl ketone was then added to thisresin solution, and it was stirred under reflux. A mixture of 5.1 partsof glycidyl methacrylate, 97.5 parts of 2-hydroxyethyl methacrylate,200.2 parts of methyl methacrylate, 122.3 parts of n-butyl acrylate and6.3 parts of azobisisobutyronitrile was then added dropwise over 2hours. After further stirring for 1 hour at a reaction temperature of120° C., the temperature was raised to 130° C. and the addition andcopolymerization reactions were completed by continuing stirring for afurther 5 hours (this reaction process is termed "Process 2" hereafter).

The resin solution obtained was a resin solution which included anacrylic graft copolymer A-1-1 having an acid value of 12 mg KOH/g, ahydroxyl value of 100 mg KOH/g, a glass transition temperature of +13°C. and a number average molecular weight of 42,000.

Preparation Examples 1-2 to 1-4

Making an Acrylic Graft Copolymer (A-1)

Acrylic graft copolymers A-1-2 to A-1-4 were made by the same method asin Preparation Example 1-1, according to the formulations in Table 1 orTable 2.

                  TABLE 1                                                         ______________________________________                                        Acrylic graft copolymer No.                                                                          A-1-1    A-1-2                                         ______________________________________                                        Process 1 (parts by weight)                                                   Solvent composition                                                           Methyl isopropyl ketone                                                                              56.4     155.2                                         Toluene                --       --                                            Monomer composition                                                           2-Hydroxyethyl methacrylate                                                                          41.8     55.7                                          Acrylic acid           11.6     15.4                                          n-Butyl acrylate       93.6     124.9                                         2-Ethylhexyl methacrylate                                                                            33.0     44.0                                          Styrene                --       --                                            Initiator                                                                     Azobisisobutyronitrile 3.6      4.8                                           t-BPOEH *1             --       --                                            t-butyl peroxybenzoate --       --                                            Reaction temperature   reflux   reflux                                        Process 2 (parts by weight)                                                   Solvent composition                                                           Methyl isopropyl ketone                                                                              328.6    227.6                                         Toluene                --       --                                            Ethylene glycol monobutyl ether                                                                      --       --                                            Monomer composition                                                           2-Hydroxyethyl methacrylate                                                                          97.5     83.6                                          Acrylic acid           --       --                                            Methyl methacrylate    200.2    171.6                                         n-Butyl acrylate       122.3    104.8                                         Styrene                --       --                                            Glycidyl methacrylate  5.1      7.0                                           Initiator                                                                     Azobisisobutyronitrile 6.3      5.4                                           t-BPOEH *1             --       --                                            t-butyl peroxybenzoate --       --                                            Reaction temperature   reflux   reflux                                        Properties of component (al-1) obtained by                                    Process 1                                                                     Acid value (mg KOH/g)  50       50                                            Hydroxyl value (mg KOH/g)                                                                            100      100                                           Glass transition temperature (°C.)                                                            -20      -20                                           Number average molecular weight                                                                      5000     4900                                          Properties of monomer combination (a2-1)                                      polymerized in Process 2                                                      Acid value (mg KOH/g)  0        0                                             Hydroxyl value (mg KOH/g)                                                                            100      100                                           Glass transition temperature (°C.)                                                            +30      +30                                           Properties of the acrylic graft copolymer                                     Acid value (mg KOH/g)  12       15                                            Hydroxyl value(mg KOH/g)                                                                             100      100                                           Glass transition temperature (°C.)                                                            +13      +8                                            Number average molecular weight                                                                      42000    32000                                         Component (al-1)/component (mm-1) (w/w)                                                              30/70    40/60                                         Component (m-3)/component (al-1) mol ratio                                                           1.0      1.0                                           ______________________________________                                         *1 tBPOEH : tButylperoxy-2-ethylhexanoate                                

                  TABLE 2                                                         ______________________________________                                        Acrylic graft copolymer No.                                                                          A-1-3    A-1-4                                         ______________________________________                                        Process 1 (parts by weight                                                    Solvent composition                                                           Methyl isopropyl ketone                                                                              --       77.9                                          Toluene                77.0     --                                            Monomer composition                                                           2-Hydroxyethyl methacrylate                                                                          27.9     41.8                                          Acrylic acid           15.4     15.4                                          n-Butyl acrylate       28.7     3.2                                           2-Ethylhexyl methacrylate                                                                            48.0     47.6                                          Styrene                --       12.0                                          Initiator                                                                     Azobisisobutyronitrile --       --                                            t-BPOEH *1             3.0      --                                            t-butyl peroxybenzoate --       3.6                                           Reaction temperature   reflux   reflux                                        Process 2 (parts by weight)                                                   Solvent composition                                                           Methyl isopropyl ketone                                                                              --       303.0                                         Toluene                156.9    --                                            Ethylene glycol monobutyl ether                                                                      150.0    --                                            Monomer composition                                                           2-Hydroxyethyl methacrylate                                                                          111.4    110.9                                         Acrylic acid           --       --                                            Methyl methacrylate    228.8    134.9                                         n-Butyl acrylate       139.8    138.2                                         Styrene                --       96.0                                          Glycidyl methacrylate  3.5      3.5                                           Initiator                                                                     Azobisisobutyronitrile --       --                                            t-BPOEH *1             9.6      --                                            t-butyl peroxybenzoate --       12.0                                          Reaction temperature   120° C.                                                                         reflux                                        Properties of component (al-1) obtained by                                    Process 1                                                                     Acid value (mg KOH/g)  100      100                                           Hydroxyl value (mg KOH/g)                                                                            100      150                                           Glass transition temperature (°C.)                                                            0        +30                                           Number average molecular weight                                                                      4900     4800                                          Properties of monomer combination (a2-1)                                      polymerized in Process 2                                                      Acid value (mg KOH/g)  0        0                                             Hydroxyl value (mg KOH/g)                                                                            100      100                                           Glass transition temperature (°C.)                                                            +30      +30                                           Properties of the acrylic graft copolymer                                     Acid value (mg KOH/g)  18       20                                            Hydroxyl value(mg KOH/g)                                                                             100      107                                           Glass transition temperature (°C.)                                                            +23      +30                                           Number average molecular weight                                                                      34000    31000                                         Component (al-1)/component (mm-1) (w/w)                                                              20/80    20/80                                         Component (m-3)/component (al-1) mol ratio                                                           1.0      1.0                                           ______________________________________                                         *1 tBPOEH : tButylperoxy-2-ethylhexanoate                                

Preparation Example 2-1

Making an Aqueous Dispersion

Ethylene glycol monobutyl ether 80 parts was added to 533 parts ofacrylic graft copolymer A-1-1 obtained in Preparation Example 1-1, andthen 205 parts of methyl isopropyl ketone was distilled off underdecreased pressure. Dimethylethanolamine 3.0 parts (equivalent to 50% ofthe carboxyl groups) was added to this polymer solution, and afterstirring 588.9 parts of deionized water was added and stirred to give aneven dispersion and obtain a milky white low-viscosity aqueousdispersion A-1-laq of the acrylic graft copolymer A-1-1 (see Table 7).

Preparation Example 2-1 to 2-4

Making an Aqueous Dispersion

Aqueous dispersions A-1-2aq to A-1-4aq of acrylic graft copolymers A-1-2to A-1-4 were obtained by the same method as in Preparation Example 2-1with the combinations shown in Table 7.

                                      TABLE 3                                     __________________________________________________________________________    Aqueous dispersion No.                                                                        A-1-1aq                                                                             A-1-2aq                                                                             A-1-3aq                                                                             A-1-4aq                                     __________________________________________________________________________    Type of acrylic graft copolymer                                                               A-1-1 A-1-2 A-1-3 A-1-4                                       Graft copolymer included                                                                      533.0 533.0 533.0 533.0                                       Ethylene glycol monobutyl ether                                                                80.0  80.0 --     80.0                                       Methyl isopropyl ketone distilled off                                                         205.0 204.0 --    205.0                                       under decreased pressure                                                      Toluene distilled off under                                                                   --    --    124.0 --                                          decreased pressure                                                            Dimethylethanolamine                                                                           3.0   3.8   4.6   5.1                                        Deionized water 588.9 587.2 586.4 586.9                                       Nature of the aqueous dispersion                                                              milky white                                                                         milky white                                                                         milky white                                                                         milky white                                 obtained        low-viscosity                                                                       low-viscosity                                                                       low-viscosity                                                                       low-viscosity                                               liquid                                                                              liquid                                                                              liquid                                                                              liquid                                      __________________________________________________________________________     Note 1: Lowviscosity means ≦1 ps at 25° C.                      Note 2: Units parts by weight                                            

Preparation Example 5-1

Making an Acrylic Graft Copolymer (A-2)

Toluene 116.4 parts was put into a reaction vessel equipped with astirrer, a temperature regulator, a cooling tube and a dropping device,stirred as the temperature was raised, and refluxed. A mixture of 41.8parts of 2-hydroxyethyl methacrylate, 18.5 parts of acrylic acid, 64.3parts of n-butyl acrylate, 55.4 parts of n-butyl methacrylate and 3.6parts of azobis-isobutyronitrile was added dropwise over 2 hours. Thenstirring was continued for a further 2 hours to complete thepolymerization (this reaction process is termed "Process (1)"hereafter).

Next, 7.4 parts of α,α-dimethylisopropenylbenzyl isocyanate and 0.1 partof dibutyltin dilaurate were put into this resin solution, and stirringwas continued for 1 hour at 80° C. (this reaction process is termed"Process (2)" hereafter).

The resin obtained was an acrylic copolymer having an acid value of 80mg KOH/g, a hydroxyl value of 100 mg KOH/g, a glass transitiontemperature of 0° C. and a number average molecular weight of 4900.

Then 266.2 parts of toluene were put into this resin solution and it wasstirred under reflux. Then a mixture of 97.4 parts of 2-hydroxyethylmethacrylate, 173.4 parts of n-butyl acrylate, 149.2 parts of methylmethacrylate and 6.3 parts of azobisisobutyronitrile was added dropwiseto this resin solution over 2 hours. The reaction was completed bycontinuing stirring for a further 2 hours (this reaction process istermed "Process (3)" below).

The resin solution obtained was a resin solution containing an acrylicgraft copolymer A-2-1 having an acid value of 24 mg KOH/g, a hydroxylvalue of 96 mg KOH/g, a glass transition temperature of +7° C. and anumber average molecular weight of 32,000 (see Table 4 to Table 6).

Preparation Example 3-2 to 3-4

Making an Acrylic Graft Copolymer (A-2)

Acrylic graft copolymers A-2-2 to A-2-4 were made by the same method asin Preparation Example 3-1, with the formulations in Table 4 to Table 6.Properties, etc., are shown in Table 4 to Table 6.

                  TABLE 4                                                         ______________________________________                                                       (parts by weight)                                              Acrylic graft copolymer No.                                                                    A-2-1   A-2-2   A-2-3 A-2-4                                  ______________________________________                                        Process 1                                                                     Solvent                                                                       Toluene          116.4   155.2   97.7  77.0                                   Methyl isobutyl ketone                                                                         --      --      --    --                                     Monomer composition                                                           2-Hydroxyethyl methacrylate                                                                    41.8    33.4    41.8  22.3                                   Acrylic acid     18.5    21.6    15.4  12.3                                   n-Butyl acrylate 64.3    105.6   78.7  22.8                                   n-Butyl methacrylate                                                                           55.4    79.4    --    50.6                                   2-Ethylhexyl methacrylate                                                                      --      --      14.1  --                                     Styrene          --      --      --    12.0                                   Polymerization initiator                                                      Azobisbutyronitrile                                                                             3.6     4.8    --    --                                     t-BPOEH *1       --      --      --     3.0                                   t-Butyl peroxybenzoate                                                                         --      --       2.3  --                                     Reaction temperature                                                                           reflux  reflux  reflux                                                                              reflux                                 Process 2                                                                     Monomers                                                                      α,α-Dimethylisopropenylbenzyl                                                       7.4     9.9     3.6   4.9                                   isocyanate                                                                    Catalyst                                                                      Dibutyltin laurate                                                                              0.1     0.2     0.1   0.1                                   Reaction temperature                                                                           80° C.                                                                         80° C.                                                                         80° C.                                                                       80° C.                          ______________________________________                                         *1 tBPOEH: tButylperoxy-2-ethylhexanoate                                 

                  TABLE 5                                                         ______________________________________                                                       (parts by weight)                                              Acrylic graft copolymer No.                                                                    A-2-1    A-2-2  A-2-3  A-2-4                                 ______________________________________                                        Process 3                                                                     Solvent                                                                       Toluene          266.2    220.9  285.0  305.4                                 Methyl isobutyl ketone                                                                         --       --     --     --                                    Monomer composition                                                           2-Hydroxyethyl methacrylate                                                                     97.4     66.9  125.3   89.1                                 Acrylic acid     --        4.6   --     --                                    Methyl methacrylate                                                                            149.2    136.4  113.1  171.1                                 n-Butyl acrylate 173.4    152.1  211.6  171.8                                 Styrene          --       --     --      48.0                                 Polymerization initiator                                                      Azobisbutyronitrile                                                                             6.3     --     --     --                                    t-BPOEH *1       --       --     --      9.6                                  t-Butyl peroxybenzoate                                                                         --        9.0    11.3  --                                    Reaction temperature                                                                           reflux   reflux reflux reflux                                ______________________________________                                         *1 tBPOEH: tButylperoxy-2-ethylhexanoate                                 

                                      TABLE 6                                     __________________________________________________________________________    Acrylic graft copolymer No. A-2-1                                                                             A-2-2                                                                             A-2-3                                                                             A-2-4                                 __________________________________________________________________________    Properties of the acrylic                                                                 Acid value                                                                              (mg KOH/g)                                                                          80  70  80  80                                    copolymer obtained in                                                                     Hydroxyl value                                                                          (mg KOH/g)                                                                          100 60  120 80                                    Process 1   Glass transition temp.                                                                  (° C.)                                                                       0   -10 -15 +20                                               Number av. mol. wt.                                                                           4900                                                                              4900                                                                              8500                                                                              4900                                  Properties of the monomer                                                                 Acid value                                                                              (mg KOH/g)                                                                          0   10  0   0                                     combination polymerized in                                                                Hydroxyl value                                                                          (mg KOH/g)                                                                          100 80  120 80                                    Process 3   Glass transition temp.                                                                  (° C.)                                                                       +10 +10 0   +20                                   Properties of the acrylic                                                                 Acid value                                                                              (mg KOH/g)                                                                          24  28  20  16                                    graft copolymer                                                                           Hydroxyl value                                                                          (mg KOH/g)                                                                          96  67  118 78                                                Glass transition temp.                                                                  (° C.)                                                                       +7  +2  -4  +20                                               Number av. mol. wt.                                                                           32000                                                                             27000                                                                             45000                                                                             38000                                             (al-2)/(mm-1) (w/w)                                                                           30/70                                                                             40/60                                                                             25/75                                                                             20/80                                             (m-5)/(a1-a) mol ratio                                                                        1.0 1.0 1.0 1.0                                   __________________________________________________________________________

Preparation Example 4-1

Making an Aqueous Dispersion

After adding 80.0 parts of ethylene glycol monobutyl ether to 533.0parts of acrylic graft copolymer A-2-1 obtained in Preparation Example3-1, 207.3 parts of toluene were distilled off at decreased pressure.Dimethylmethanolamine 6.1 parts was added to this polymer solution(equivalent to 50% of the carboxyl groups), and after stirring 588.2parts of deionized water was added and stirred to give a uniformdispersion, and obtain a milky white low-viscosity aqueous dispersionA-2-laq of acrylic graft copolymer A-2-1 (see Table 7).

Preparation Examples 4-2 to 4-4

Making an Aqueous Dispersion

Aqueous dispersions A-2-2aq to A-2-4aq of acrylic graft copolymers A-2-2to A-2-4 were obtained by the same method as in Preparation Example 4-1with the combinations in Table 7.

                                      TABLE 7                                     __________________________________________________________________________    Aqueous dispersion No.                                                                        A-2-1aq                                                                             A-2-2aq                                                                             A-2-3aq                                                                             A-2-4aq                                     __________________________________________________________________________    Type of acrylic graft copolymer                                                               A-2-1 A-2-2 A-2-3 A-2-4                                       Graft copolymer included                                                                      533.0 533.0 533.0 533.0                                       Ethylene glycol monobutyl ether                                                                80.0  80.0 --     80.0                                       Methyl isopropyl ketone distilled off                                                         207.3 200.5 204.0 203.8                                       under decreased pressure                                                      Toluene distilled off under                                                                   --    --    --    --                                          decreased pressure                                                            Dimethylethanolamine                                                                           6.1   7.1   5.1   4.1                                        Deionized water 589.0 580.4 585.9 586.7                                       Nature of the aqueous dispersion                                                              milky white                                                                         milky white                                                                         milky white                                                                         milky white                                 obtained        low-viscosity                                                                       low-viscosity                                                                       low-viscosity                                                                       low-viscosity                                               liquid                                                                              liquid                                                                              liquid                                                                              liquid                                      __________________________________________________________________________

Preparation Example 5-1

Making Internally Non-Crosslinked Acrylic Fine Particle (B)

Deionized water 606 parts and 3.0 parts of Ereminol ES-12 (surfactant;trade name Sanyo Chemicals) were put into a 4-mouthed flask fitted witha stirrer, a thermometer, a reflux cooling tube and a tube forintroducing nitrogen gas, and held at 80° C. stirred in a stream ofnitrogen. Then 250.6 parts of a mixture (1) of 47.8 parts of n-butylacrylate, 71.6 parts of methyl methacrylate, 30.6 parts of2-hydroxyethyl acrylate, 0.6 parts of Ereminol ES-12 and 100 parts ofdeionized water was formed into a pre-emulsified dispersion and,stirring at 80° C., a polymerization initiator (1) of 0.6 parts ofammonium persulfate dissolved in 19.4 parts of deionized water was addeddropwise in parallel with this emulsion over 2 hours. The mixture wasstirred at 80° C. for a further 1 hour to mature the core of the acrylicfine particles. Then 100.4 parts of pre-emulsified dispersion of amixture (2) of 30 parts of n-butyl acrylate, 10.8 parts of2-hydroxyethyl acrylate, 9.2 parts of methacrylic acid, 0.4 parts ofEreminol ES-12 and 50 parts of deionized water, and a polymerizationinitiator (2) of 0.2 parts of ammonium persulfate dissolved in 19.8parts of deionized water were added dropwise in parallel over 1 hour.The reaction was completed by stirring at 80° C. for a further 2 hours,to obtain internally non-crosslinked acrylic fine particles B-1 havingan acid value of 30 mg KOH/g, a hydroxyl value of 100 mg KOH/g, a glasstransition temperature of +3° C. and a mean particle size of 60 nm. Themean particle size was determined in an aqueous medium using a NICOMP370 Sub-micron Particle Sizer (trade mark Pacific Scientific InstrumentCompany) (see Table 8).

Preparation Example 5-2 to 5-4

Making Internally Non-Crosslinked Acrylic Fine Particles (B)

Internally non-crosslinked acrylic fine particles B-2 to B-4 were madeby the same method as in Preparation Example 5-1 with the combinationsshown in Table 8.

                  TABLE 8                                                         ______________________________________                                        Acrylic fine particle No.                                                                        B-1    B-2     B-3  B-4                                    ______________________________________                                        Put into the reaction tank                                                    Deionized water    606    606     606  606                                    Ereminol ES-12 *1  3      3       3    3                                      Mixture (1)                                                                   n-Butyl acrylate   47.8   46.7    46.4 67.5                                   Methyl methacrylate                                                                              71.6   71.6    71.6 82.5                                   2-Hydroxyethyl acrylate                                                                          30.6   31.7    32.0 --                                     Ereminol ES-12 *1  0.6    0.6     0.6  0.6                                    Deionized water    100    100     100  100                                    Polymerization initiator (1)                                                  Ammonium persulphate                                                                             0.6    0.6     0.6  0.6                                    Deionized water    19.4   19.4    19.4 19.4                                   Mixture (2)                                                                   n-Butyl acrylate   30     25.O    10   28.4                                   2-Hydroxyethyl acrylate                                                                          10.8   9.7     9.4  12.4                                   Methacrylic acid   9.2    15.3    30.6 9.2                                    Ereminol ES-12 *1  0.4    0.4     0.4  0.4                                    Deionized water    50     50      50   50                                     Polymerization initiator (2)                                                  Ammonium sulfate   0.2    0.2     0.2  0.2                                    Deionized water    19.8   19.8    19.8 19.8                                   Properties of the internally                                                  non-crosslinked acrylic fine                                                  particles (B)                                                                 Acid value (mg KOH/g)                                                                            30     50      100  30                                     Hydroxyl value (mg KOH/g)                                                                        100    100     100  30                                     Glass transition temperature (°C.)                                                        3      9       26   4                                      Mean particle size (nm)                                                                          60     80      100  60                                     ______________________________________                                         *1 Trade name Sanyo Chemicals                                            

Embodiments 1-11

Metallic water-based paint compositions having a solids content of 32 wt% were prepared on the basis of the combinations shown in Table 9 toTable 11 by adding an aqueous dispersion obtained in Preparation Example2-1 to 2-4 and Preparation Example 4-1 to 4-4, internallynon-crosslinked acrylic fine particles B-1 to B-4 obtained inPreparation Example 5-1 to 5-4, aluminum paste (Alupaste 0539X; specialprocessed aluminum for water-based paint; heat residue 69 wt % (tradename Toyo Aluminum), an amino resin (Cymel 327; trade name MitsuiScitec), an organic thickener swelled by alkalis (Primal ASE-60; tradename Rohm & Haas), dimethylethanolamine and deionized water. When thesolids content of the water-based paint composition was ≦32 wt %viscosity was adjusted without adding deionized water. These metallicwater-based paint compositions were adjusted to a viscosity of 15±2 psusing a B type viscosimeter at a rotation rate of 6 rpm, by addingwater, and evaluated according to the aforementioned methods.

The results for appearance and performance of the resulting paint films,and the results for storage stability, are shown in Table 12.

                  TABLE 9                                                         ______________________________________                                                       (parts by weight)                                              Embodiment No.   1       2       3     4                                      ______________________________________                                        Aqueous dispersion                                                            A-1-1aq          517.2   --      --    --                                     A-1-2aq          --      517.2   --    --                                     A-1-3aq          --      --      517.2 --                                     A-1-4aq          --      --      --    517.2                                  A-2-1aq          --      --      --    --                                     A-2-2aq          --      --      --    --                                     A-2-3aq          --      --      --    --                                     A-2-4aq          --      --      --    --                                     Acrylic fine particles                                                        B-1              137.9   137.9   137.9 137.9                                  B-2              --      --      --    13                                     B-3              --      --      --    --                                     B-4              --      --      --    --                                     Dimethylethanolamine                                                                           3.3     3.5     3.6   3.7                                    Cymel 327 *1     91.9    91.9    91.9  91.9                                   Aluminum paste *2                                                                              59.9    59.9    59.9  59.9                                   Ethylene glycol monobutyl ether                                                                60.6    60.6    60.6  60.6                                   Thickener *3     4.7     4.7     4.7   4.7                                    Deionized water  124.5   124.3   124.2 124.1                                  Deionized water to adjust                                                                      15.9    32.2    66.7  103.4                                  viscosity                                                                     Total            1015.9  1032.2  1066.7                                                                              1103.4                                 Paint solids     31.5%   31.0%   30.0% 29.0%                                  ______________________________________                                         *1 Trade name Mitsui Scitec                                                   *2 Alupaste 0539X (trade name Toyo Aluminum)                                  *3 Primal ASE60 (trade name Rohm & Haas)                                 

                  TABLE 10                                                        ______________________________________                                                       (parts by weight)                                              Embodiment No.   5       6       7     8                                      ______________________________________                                        Aqueous dispersion                                                            A-1-1aq          --      --      --    --                                     A-1-2aq          --      --      --    --                                     A-1-3aq          --      --      --    --                                     A-1-4aq          --      --      --    --                                     A-2-1aq          517.2   --      --    --                                     A-2-2aq                  517.2   --    --                                     A-2-3aq                          517.2 --                                     A-2-4aq                                517.2                                  Acrylic fine particles                                                        B-1              137.9   137.9   137.9 137.9                                  B-2              --      --      --    --                                     B-3              --      --      --    --                                     B-4              --      --      --    --                                     Dimethylethanolamine                                                                           3.9     4.1     3.7   3.5                                    Cymel 327 *      91.9    91.9    91.9  91.9                                   Aluminum paste *2                                                                              59.9    59.9    59.9  59.9                                   Ethylene glycol monobutyl ether                                                                60.6    60.6    60.6  60.6                                   Thickener *3     4.7     4.7     4.7   4.7                                    Deionized water  123.9   123.7   124.1 124.3                                  Deionized water to adjust                                                                      122.8   142.9   103.4 49.2                                   viscosity                                                                     Total            1122.8  1142.9  1103.4                                                                              1049.2                                 Paint solids     28.5%   28.0%   29.0% 30.5%                                  ______________________________________                                         *1 Trade name Mitsui Scitec                                                   *2 Alupaste 0539X (trade name Toyo Aluminum)                                  *3 Primal ASE60 (trade name Rohm & Haas)                                 

                  TABLE 11                                                        ______________________________________                                                        (parts by weight)                                             Embodiment No.    9        10      11                                         ______________________________________                                        Aqueous dispersion                                                            A-1-1aq           517.2    517.2   --                                         A-1-2aq           --       --      --                                         A-1-3aq           --       --      --                                         A-1-4aq           --       --      --                                         A-2-1aq           --       --      517.2                                      A-2-2aq           --       --      --                                         A-2-3aq           --       --      --                                         A-2-4aq           --       --      --                                         Acrylic fine particles                                                        B-1               --       --      --                                         B-2               137.9    --      --                                         B-3               --       137.9   --                                         B-4               --               137.9                                      Dimethylethanolamine                                                                            3.6      3.7     3.5                                        Cymel 327         91.9     91.9    91.9                                       Aluminum paste *2 59.9     59.9    59.9                                       Ethylene glycol monobutyl ether                                                                 60.6     60.6    60.6                                       Thickener *3      4.7      4.7     4.7                                        Deionized water   124.2    124.1   124.3                                      Deionized water to adjust                                                                       66.7     142.9   122.8                                      viscosity                                                                     Total             1066.7   1142.9  1122.8                                     Paint solids      30.0%    28.0%   28.5%                                      ______________________________________                                         *1 Trade name Mitsui Scitec                                                   *2 Alupaste 0539X (trade name Toyo Aluminum)                                  *3 Primal ASE60 (trade name Rohm & Haas)                                 

                  TABLE 12                                                        ______________________________________                                        Embodiment No.                                                                           1     2     3   4   5   6   7   8   9   10  11                     ______________________________________                                        Dry film                                                                      thickness                                                                     Undercoat (μm)                                                                        15    16    15  15  16  15  15  16  15  15  15                     Clear coat (μm)                                                                       40    40    41  41  41  40  41  40  41  40  41                     Painted                                                                       appearance                                                                    60° Gloss                                                                         93    93    95  94  93  95  94  94  95  93  95                     Smoothness ∘                                                                       ∘                                                                       ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘          Sagging    ∘                                                                       ∘                                                                       ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘          Al bittiness                                                                             ∘                                                                       ∘                                                                       ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘          Paint film                                                                    performance                                                                   Water-resistance                                                                         ∘                                                                       ∘                                                                       ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘          Resilience ∘                                                                       ∘                                                                       ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘          Resistance to                                                                            ∘                                                                       ∘                                                                       ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘          chemicals                                                                     Storage stability                                                                        ∘                                                                       ∘                                                                       ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘          ______________________________________                                    

Comparison Preparation Examples 1-4

1) Making an Acrylic Graft Copolymer

Acrylic graft copolymers E-1 to E-4 were made by the same method as inPreparation Example 1 according to the formulations in Table 13 andTable 14. In E-1 the acid values of the hydrophilic acrylic copolymer(component (a1-1)) which becomes the stabilizing layer and of the finalproduct are too high; in E-2 the hydroxyl value of the hydrophilicacrylic copolymer (component (a1-1)) which becomes the stabilizing layeris too low; in E-3 the acid values of the hydrophobic acrylic copolymer(monomer combination (a2-1) which becomes the dispersion layer and ofthe final product are too high; and in E-4 the hydroxyl values of thehydrophobic acrylic copolymer (monomer combination (a2-1) which becomesthe dispersion layer and of the final product are too high.

                  TABLE 13                                                        ______________________________________                                        Acrylic graft copolymer No.                                                                          E-1      E-2                                           ______________________________________                                        Process 1 (parts by weight)                                                   Solvent composition                                                           Methyl isopropyl ketone                                                                              95.5     --                                            Toluene                --       95.5                                          Monomer composition                                                           2-Hydroxyethyl methacrylate                                                                          34.8     3.5                                           Acrylic acid           28.9     19.4                                          n-Butyl acrylate       50.6     5O.3                                          n-Butyl methacrylate   --       --                                            Methyl methacrylate    --       76.8                                          2 -Ethylhexyl methacrylate                                                                           35.7     --                                            Initiator                                                                     t-Butyl peroxybenzoate 4.5      4.5                                           Reaction temperature   reflux   reflux                                        Process 2 (parts by weight)                                                   Solvent composition                                                           Methyl isopropyl ketone                                                                              286.6    --                                            Toluene                --       286.6                                         Monomer composition                                                           2-Hydroxyethyl methacrylate                                                                          104.4    104.4                                         n-Butyl methacrylate   --       --                                            Acrylic acid           --       --                                            Methyl methacrylate    214.5    214.5                                         n-Butyl acrylate       131.1    131.1                                         Glycidyl methacrylate  4.4      4.4                                           Initiator                                                                     t-BPOEH *1             9.0      9.0                                           Reaction temperature   reflux   reflux                                        Properties of component (al-1) obtained by                                    Process 1                                                                     Acid value (mg KOH/g)  150      100                                           Hydroxyl value (mg KOH/g)                                                                            100      10                                            Glass transition temperature (°C.)                                                            0        +30                                           Number average molecular weight                                                                      4700     4800                                          Properties of monomer combination (a2-1)                                      polymerized in Process 2                                                      Acid value (mg KOH/g)  0        0                                             Hydroxyl value (mg KOH/g)                                                                            100      100                                           Glass transition temperature (°C.)                                                            +30      +30                                           Properties of the acrylic graft copolymer                                     Acid value (mg KOH/g)  34       22                                            Hydroxyl value (mg KOH/g)                                                                            100      78                                            Glass transition temperature (°C.)                                                            +22      +30                                           Number average molecular weight                                                                      31000    31000                                         Component (al-1)/component (mm-1) (w/w)                                                              25/75    25/75                                         Component (m-3)/component (al-1) mol ratio                                                           1.0      1.0                                           ______________________________________                                         *1 tBPOEH : tButylperoxy-2-ethylhexanoate                                

                  TABLE 14                                                        ______________________________________                                        Acrylic graft copolymer No.                                                                          E-3      E-4                                           ______________________________________                                        Process 1 (parts by weight)                                                   Solvent composition                                                           Methyl isopropyl ketone                                                                              95.5     95.5                                          Toluene                --       --                                            Monomer composition                                                           2-Hydroxyethyl methacrylate                                                                          34.8     34.8                                          Acrylic acid           19.4     19.4                                          n-Butyl acrylate       35.8     35.8                                          n-Butyl methacrylate   --       --                                            Methyl methacrylate    --       --                                            2 -Ethylhexyl methacrylate                                                                           60.0     60.0                                          Initiator                                                                     t-Butyl peroxybenzoate 4.5      4.5                                           Reaction temperature   reflux   reflux                                        Process 2 (parts by weight)                                                   Solvent composition                                                           Methyl isopropyl ketone                                                                              286.7    286.6                                         Toluene                --       --                                            Monomer composition                                                           2-Hydroxyethyl methacrylate                                                                          104.4    208.8                                         n-Butyl methacrylate   --       --                                            Acrylic acid           17.3     --                                            Methyl methacrylate    170.7    132.0                                         n-Butyl acrylate       157.5    109.2                                         Glycidyl methacrylate  4.4      4.4                                           Initiator                                                                     t-BPOEH *1             9.0      9.0                                           Reaction temperature   reflux   reflux                                        Properties of component (al-1) obtained by                                    Process 1                                                                     Acid value (mg KOH/g)  100      100                                           Hydroxyl value (mg KOH/g)                                                                            100      100                                           Glass transition temperature (° C.)                                                           0        0                                             Number average molecular weight                                                                      4700     4700                                          Properties of monomer combination (a2-1)                                      polymerized in Process 2                                                      Acid value (mg KOH/g)  30       0                                             Hydroxyl value (mg KOH/g)                                                                            100      200                                           Glass transition temperature (°C.)                                                            +20      +30                                           Properties of the acrylic graft copolymer                                     Acid value (mg KOH/g)  44       22                                            Hydroxyl value (mg KOH/g)                                                                            100      175                                           Glass transition temperature (°C.)                                                            +15      +22                                           Number average molecular weight                                                                      31000    31000                                         Component (al-1)/component (mm-1) (w/w)                                                              25/75    25/75                                         Component (m-3)/component (al-1) mol ratio                                                           1.0      1.0                                           ______________________________________                                         *1 tBPOEH : tButylperoxy-2-ethylhexanoate                                

2) Making an aqueous suspension

Using the acrylic graft copolymers E-1 to E-4 obtained in 1) above,aqueous emulsions E-1aq to E-4aq of acrylic graft copolymers E-1 to E-4were made by the same method as in Preparation Example 2-1 with thecombinations shown in Table 15.

                                      TABLE 15                                    __________________________________________________________________________    Aqueous dispersion No.                                                                        E-1aq E-2aq E-3aq E-4aq                                       __________________________________________________________________________    Type of acrylic graft copolymer                                                               E-1   E-2   E-3   E-4                                         Graft copolymer included                                                                      533.0 533.0 533.0 533.0                                       Ethylene glycol monobutyl ether                                                                80.0  80.0 --     80.0                                       Methyl isopropyl ketone distilled off                                                         203.0 --    203.0 --                                          under decreased pressure                                                      Toluene distilled off under                                                                   --    203.0 --    203.0                                       decreased pressure                                                            Dimethylethanolamine                                                                           8.6   5.6   11.1  5.6                                        Deionized water 581.4 584.4 578.9 584.4                                       Nature of the aqueous dispersion                                                              milky white                                                                         milky white                                                                         milky white                                                                         milky white                                 obtained        low-viscosity                                                                       low-viscosity                                                                       low-viscosity                                                                       low-viscosity                                               liquid                                                                              liquid                                                                              liquid                                                                              liquid                                      __________________________________________________________________________     Note 1: Lowviscosity means ≦1 ps at 25° C.                      Note 2: Units parts by weight                                            

Comparison Preparation Examples 5 and 6

Making Internally Non-Crosslinked Acrylic Fine Particles

Internally non-crosslinked acrylic fine particles were made by the samemethod as in Preparation Example 5, according to the formulations ofTable 16. In the case of internally non-crosslinked acrylic fineparticles F-1 the acid value was too low, and in F-2 the hydroxyl valuewas too high.

                  TABLE 16                                                        ______________________________________                                        Acrylic fine particle No.                                                                            F-1      F-2                                           ______________________________________                                        Put into the reaction tank                                                    Deionized water        606      606                                           Ereminol ES-12 *1      3        3                                             Mixture (1)                                                                   n-Butyl acrylate       47.8     16.8                                          Methyl methacrylate    71.6     40.0                                          2-Hydroxyethyl acrylate                                                                              30.6     93.2                                          Ereminol ES-12 *1      0.6      0.6                                           Deionized water        100      100                                           Polymerization initiator (1)                                                  Ammonium persulphate   0.6      0.6                                           Deionized water        19.4     19.4                                          Mixture (2)                                                                   n-Butyl acrylate       37.7     10                                            2-Hydroxyethyl acrylate                                                                              10.8     30.8                                          Methacrylic acid       1.5      9.2                                           Ereminol ES-12 *1      0.4      0.4                                           Deionized water        50       50                                            Polymerization initiator (2)                                                  Ammonium sulfate       0.2      0.2                                           Deionized water        19.8     19.8                                          Properties of the internally                                                  non-crosslinked acrylic fine                                                  particles (B)                                                                 Acid value (mg KOH/g)  5        30                                            Hydroxyl value (mg KOH/g)                                                                            100      300                                           Glass transition temperature (°C.)                                                            -4       2                                             Mean particle size (nm)                                                                              60       70                                            ______________________________________                                         *1 Trade name Sanyo Chemicals                                            

Comparison Examples 1-6

Water-based paint compositions were prepared as in the embodiments basedon the combinations in Table 17 and Table 18. The water-based paintcompositions obtained were evaluated by the same methods as for theembodiments. The results are shown in Table 19.

                  TABLE 17                                                        ______________________________________                                                        (parts by weight)                                             Comparison Example No.                                                                          1        2       3                                          ______________________________________                                        Aqueous dispersion                                                            E-1aq             517.2    --      --                                         E-2aq             --       517.2   --                                         E-3aq             --       --      517.2                                      E-4aq             --       --      --                                         A-1-1aq           --       --      --                                         Acrylic fine particles                                                        B-1               137.9    137.9   137.9                                      F-1               --       --      --                                         F-2               --       --      --                                         Dimethylethanolamine                                                                            4.9      3.5     5.2                                        Cymel 327 *1      91.9     91.9    91.9                                       Aluminum paste *2 59.9     59.9    59.9                                       Ethylene glycol monobutyl ether                                                                 60.6     60.6    60.6                                       Thickener *3      4.7      4.7     4.7                                        Deionized water   122.9    124.3   122.6                                      Deionized water to adjust                                                                       454.5    0.0     561.0                                      viscosity                                                                     Total             1454.5   1000.0  1561.0                                     Paint solids      22.0%    32.0%   20.5%                                      ______________________________________                                         *1 Trade name Mitsui Scitec                                                   *2 Alupaste 0539X (trade name Toyo Aluminum)                                  *3 Primal ASE60 (trade name Rohm & Haas)                                 

                  TABLE 18                                                        ______________________________________                                                        (parts by weight)                                             Comparison Example No.                                                                          4        5       6                                          ______________________________________                                        Aqueous dispersion                                                            E-1aq             --       --      --                                         E-2aq             --       --      --                                         E-3aq             --       --      --                                         E-4aq             517.2    --                                                 A-1-1aq           --       517.2   517.2                                      Acrylic fine particles                                                        B-1               137.9    --      --                                         F-1               --       137.9   --                                         F-2               --       --      137.9                                      Dimethylethanolamine                                                                            3.5      3.2     3.3                                        Cymel 327         91.9     91.9    91.9                                       Aluminum paste *2 59.9     59.9    59.9                                       Ethylene glycol monobutyl ether                                                                 60.6     60.6    60.6                                       Thickener *3      4.7      4.7     4.7                                        Deionized water   124.3    124.6   124.5                                      Deionized water to adjust                                                                       142.9    0.0     66.7                                       viscosity                                                                     Total             1142.9   1000.0  1066.7                                     Paint solids      28.0%    32.0%   30.0%                                      ______________________________________                                         *1 Trade name Mitsui Scitec                                                   *2 Alupaste 0539X (trade name Toyo Aluminum)                                  *3 Primal ASE60 (trade name Rohm & Haas)                                 

                  TABLE 19                                                        ______________________________________                                        Embodiment No. 1     2       3   4     5   6                                  ______________________________________                                        Dry film thickness                                                            Undercoat (μm)                                                                            15    16      15  1S    16  15                                 Clear coat (μm)                                                                           40    40      41  41    41  40                                 Painted appearance                                                            60° Gloss                                                                             90    91      90  92    89  93                                 Smoothness     ∘                                                                       ∘                                                                         ∘                                                                     ∘                                                                       ∘                                                                     ∘                      Sagging        x     ∘                                                                         x   ∘                                                                       ∘                                                                     ∘                      A1 bittiness   ∘                                                                       ∘                                                                         ∘                                                                     ∘                                                                       x   ∘                      Paint film performance                                                        Water-resistance                                                                             ∘                                                                       ∘                                                                         x   x     ∘                                                                     x                                  Resistance to chemicals                                                                      ∘                                                                       x       ∘                                                                     ∘                                                                       ∘                                                                     ∘                      Storage stability                                                                            ∘                                                                       ∘                                                                         ∘                                                                     ∘                                                                       ∘                                                                     ∘                      ______________________________________                                    

It is evident from the results of Table 19 that with Comparison Example1 the proportion of painted solids of the resulting water-based paintcomposition is low so that sagging is produced and paint film appearanceis inferior because the acid value of the acrylic graft copolymer E-1 istoo high and the acid value of the stabilizing layer constituent ofgraft copolymer E-1 is too high.

With Comparison Example 2 the resistance of the resulting paint film tochemicals is inferior because the hydroxyl value of the stabilizinglayer constituent of the acrylic graft copolymer E-2 is too low.

With Comparison Example 3 the proportion of painted solids of theresulting water-based paint composition is low so that sagging isproduced and paint film appearance is inferior because the acid value ofthe acrylic graft copolymer E-3 is too high and the acid value of thedispersion layer constituent of graft copolymer E-3 is too high.

With Comparison Example 4 the water-resistance of the resulting paintfilm is inferior because the hydroxyl value of the acrylic graftcopolymer E-4 is too high and the hydroxyl value of the dispersion layerconstituent of the acrylic graft copolymer E-4 is too high.

With Comparison Example 5 the pseudoplastic properties of the resultingwater-based paint composition are weak, so that aluminum bittiness isproduced in the resulting paint film and appearance is inferior, becausethe acid value of the acrylic fine particles F-1 is low.

With Comparison Example 6 the resulting paint film is inferior inwater-resistance because the hydroxyl value of the acrylic fineparticles F-2 is high.

We claim:
 1. A water-based paint composition comprising(A) awater-dispersible acrylic graft copolymer having an acid value of from10 to 28 mg KOH/g and a hydroxyl value of 50-150 mg KOH/g, wherein (A)is a graft copolymer of(a1) an acrylic copolymer of α,β-ethylenicunsaturated monomers including an α,β-ethylenic unsaturated carboxylicacid, said copolymer having an acid value of 35-120 mg KOH/g and ahydroxyl value of 50-150 mg KOH/g, and (a2) an acrylic copolymer ofα,β-ethylenic unsaturated monomers, said copolymer having an acid valueof ≦15 mg KOH/g and a hydroxyl value of 50-150 mg KOH/g, wherein (a1)and (a2) are graft copolymerized via chemical linkages, and (B)internally non-crosslinked acrylic fine particles comprising a copolymerdifferent from the water-dispersible acrylic graft copolymer (A) andmade by emulsion polymerization of α,β-ethylenic unsaturated monomers(b1), said copolymer having an acid value of 30-200 mg KOH/g and ahydroxyl value of 15-200 mg KOH/g, wherein the water-dispersible acrylicgraft copolymer (A), is present in an amount between 10 and 90% byweight, and the internally non-crosslinked acrylic fine particles (B)are present in an amount between 10 and 90% by weight, based on totalresin solids in the water-based paint composition.
 2. A water-basedpaint composition according to claim 1, further comprising an aminoresin (C) of a number-average molecular weight of ≦1000, present in anamount of 10-40% by weight, based on the weight of the total resinsolids in the water-based paint composition.
 3. A water-based paintcomposition according to claims 1 or 2, further comprising (D) anorganic thickener swelled by alkalis in an amount of 0.1-5 % by weightbased on the weight of the total resin solids in the water-based paintcomposition.
 4. A water-based paint composition according to one ofclaims 1-3, wherein the glass transition temperature of the acryliccopolymer (a1) is -20 to +50° C. and its number average molecular weightis 4500-9000, the glass transition temperature of the water-dispersibleacrylic graft copolymer (A) is -20 to +50° C. and its number averagemolecular weight is 10,000 to 100,000, and the mean particle size of theinternally non-crosslinked acrylic fine particles (B) in an aqueousmedium is 20-150 nm.